Gulp doesn't work and returns nothing, just opens the gulp.js file

I wanted to begin to use Gulp for the common simple tasks like SCSS compiling. But once I ran Gulp, it simply opened the file gulp.js.

After many searches and tries, I reduced all to the minimum possible:
I uninstalled NodeJS, rebooted, and reinstalled it. Then I reinstalled Gulp globally. Then I created a folder test with inside a index.html, and a folder scss with inside my style.scss. I did cd myfolder in the console and installed Gulp inside (npm init then npm install gulp --save-dev). I also created the simplest gulp.js file:

var gulp = require('gulp');

gulp.task('default', function() {
console.log('Hello');
});

When I write "gulp" in the console, it does the same: it opens the gulp.js file without doing anything. It doesn't return any value either.